In the process of borehole drilling, a drill string is deformed into a helix form under the effect of torque, and then collides and rubs against the wall of borehole during rotation, in which the drill string readily tends to be damaged prematurely under the action of wear and alternating load, thereby leading to accidents such as rapture of the drilling tool, etc. within the borehole, which brings a great loss to the whole project. With the drilling depth increased, the length of the drill string increases, and the rate of energy consumed by the drill string against various frictional resistances within the borehole increases in the process of transmitting drilling pressure and torque, therefore drill rig is required to provide a greater torque. When the borehole depth reaches a certain value, it is necessary to add downhole power tools in proximity to the drill bit in order to provide torque for the high speed rotation of the bit, and an upper drill string provides a reverse torque for the bit by a slow rotation of a ground rotary table (TDS). Obviously, although the reverse torque generated by the rock-crushing, which is by means of the rotation of the drill tool within the borehole, may endanger the whole drill string and the ground apparatus, the drilling process needs to first satisfy the environment condition of reverse torque in order to be implemented smoothly. Meanwhile, an individual drill bit requires surrounding rocks to provide the corresponding reverse torque for the rock in contact with the bit while the rock is being crushed, thereby there exists a higher requirement for surrounding rocks of the borehole wall. In case of drilling a crushed stratum, the surrounding rocks cannot provide a sufficient reverse torque by an inherent binding force for the rock in contact with the drill bit, and thereby break away from the borehole wall in a form of block structures. In addition, the borehole wall is stirred by a local turbulence generated by the mud circulated due to rotation of the drill string, and the borehole may be enlarged. When drilling through the hard large granular glutenite, the slipping gravel can easily enter the water gap of borehole and produce great torque with other gravel bridges, which will easily lead to the caving of drill bit teeth. The stability of the borehole wall is crucial for a smooth implementation of the borehole drilling, and the stability of the borehole wall is bound up with the disturbing degree to the borehole wall by the subjective drilling tool besides depending on the integrity of the objective stratum and the lithologic character. For this reason, domestic and foreign experts have tried every means to reduce disturbing to the borehole wall caused by the drill string. In addition, for the purpose of driving the bit to drill by crushing the rocks, a large and costly ground drilling apparatus should be equipped together with matched complex drilling tools and process with huge investment, in which the energy used for crushing rocks only accounts for about 10% of the total energy consumed by the drilling system, and a majority of the energy is used for operation of the apparatus.
Until now there have been few researches on the torque balanced drilling tool system at home and aboard. The scientific research is mostly directed to improve the drilling efficiency as far as possible in terms of structure, material, and process to save the drilling cost, which is based on the traditional drilling tool system, and some relating theoretical results have been achieved. In terms of the reduction of the disturbing to the borehole wall from the drill string, etc., the Brown Petroleum Tools Company in US manufactured the first set of the prototype of workover rig with coiled tubing in the 1960s, in which the power drilling tools are disposed at a position near the drill bit within the borehole. The coiled tubing only provides the reverse torque and the power source of the mud but with no rotation, which significantly reduces the disturbing to the borehole wall. The drill rig with coiled tubing was applied to the drilling from 1990s, and until 2011, the total number of drill rigs with coiled tubing around the world exceeded 1881. The application fields of the coiled-tubing drilling technology almost cover every aspect of small-diameter drilling boreholes. There are oversea companies such as Foremost Company, Baker Hughes Company and Shell Company, etc. And most of the domestic companies mainly aim to absorb imported technologies. At present, the companies who devote the research on coiled-tubing drilling technology include Honghua Petroleum Equipment co., LTD of Sichuan, Han River machinery research institute of CNPC, Great Wall Drilling Engineering co., LTD, Drilling Engineering Institute of Technology of CNPC and so on. However, since the coiled-tubing drilling technology fails to eliminate radically the harmful effects to the coiled tubing caused by the reverse torque, the working life of the coiled tubing is shorter than that of a conventional drill string.
Therefore, a new technique is needed to solve this problem.